Temperature

BCRMSE

    • For both the 00 and 12 UTC initializations, a diurnal trend is seen in the distribution of BCRMSE values, which generally range between 2.2 - 3.7 C, depending on the temporal aggregation.
    • For the annual, fall and winter aggregations, the largest errors occur for forecasts valid during the early morning hours, whereas, for the spring and summer aggregations the largest errors occur for forecasts valid during the afternoon. The reverse is true for the smallest errors within the seasonal aggregations.
    • A general increase in BCRMSE is noted with forecast lead time

Bias

    • A statistically significant (SS) cold bias is seen at all forecast lead times during the summer and spring aggregations for both 00 and 12 UTC initializations. For many of the forecast lead times, the confidence intervals (CIs) encompass zero for the fall and winter aggregations. However, when a SS bias is noted for the fall season, which is observed more often for the 00 UTC initializations, it is always too cold; for the the winter season, SS biases are always too cold for the 00 UTC initializations and too warm (during the overnight hours) for the 12 UTC initializations.
    • The amplitude of the bias does not generally increase with forecast lead time, for any temporal aggregation.

Dew Point Temperature

BCRMSE

    • Regardless of the initialization hours, all temporal aggregations reveal a diurnal trend and an increase in BCRMSE values with lead time. The BCRMSE values generally range from 2.2 - 3.8 C.
    • For the annual, spring, summer and fall aggregations, the largest errors occur for forecasts valid between 21 - 00 UTC, while the largest error for the winter aggregation occurs around 12 UTC. In general, the smallest errors are noted between 06 and 12 UTC valid times for all temporal aggregations except winter, which is lowest for forecasts valid closer to 15 - 18 UTC.

Bias

    • Generally, when there is a SS bias seen, it is a high bias regardless of initialization time or temporal aggregation. The only exceptions are the 6-9 hour forecast lead times for the summer season which have a SS low bias.
    • A diurnal trend is noted; the highest bias is generally seen at valid times near 00 UTC and the lowest bias near 12 UTC.

Wind

BCRMSE

    • For both initializations, the BCRMSE values range from approximately 1.7 - 2.5 m/s and increase with lead time.
    • For all temporal aggregations, the largest BCRMSE values are seen for times valid at 00 UTC, regardless of initialization time, while the smallest errors are around the 09 - 12 UTC valid times.

Bias

    • A SS high wind speed bias is noted for all forecast lead times, regardless of initialization hour or temporal aggregation.
    • For both the 00 and 12 UTC initializations, a very large diurnal cycle is noted with SS larger high bias during the overnight hours compared to the daytime hours.

3-hour Precipitation Accumulation

GSS

    • Regardless of initialization time or forecast lead time examined, the highest GSS values are seen at the lowest precipitation threshold and steadily decrease to near-zero for higher thresholds. The number of observed events (base rate) by threshold has a similar trend. The highest GSS values tend to occur during the fall and winter seasons at the 12-hour lead time and decrease with longer lead time and higher thresholds; the lowest GSS values are associated with the summer season.

Frequency Bias

    • For both the 00 and 12 UTC initializations, a high bias is generally noted for the lowest thresholds, regardless of forecast lead time or temporal aggregation. This general high bias transitions to a general low bias at the highest thresholds for the year, summer and spring aggregations, and occasionally for the fall as well. The threshold at which this transition occurs depends strongly on the seaonal aggregation, intialization hour and forecast lead time.
    • For the winter aggregation there are no SS low biases noted for the highest thresholds.
    • The CIs for the winter and fall seasons in particular are quite wide and often encompass one at the higher thresholds indicating lower confidence due to the relatively few number of observed events.

24-hour Precipitation Accumulation

GSS

    • A general decrease in GSS with increasing threshold and lead time, similar to that seen for 3-hour precipitation accumulations, is noted for all temporal aggregations except winter. Again, a similar trend is noted in the base rate, with very few observed events of 3" accumulations in 24 hours.
    • For the winter aggregation, the median GSS value does not decrease as dramatically for the higher threshold values; however, the CIs associated with those values are very large, indicating a low confidence - likely related to the low base rate during winter season for the higher thresholds.

Frequency Bias

    • The spring and winter aggregations display a SS high bias for the low thresholds, which continues for the mid-range thresholds for the winter season forecasts intiailized at 00 UTC.
    • For the lowest threshold, the summer aggregation also has a SS high bias, but this transitions to a SS low bias for the mid-range thresholds.
    • In general, the CIs for all other thresholds regardless of initialization time or forecast hour (including all thresholds for the fall aggregation) encompass one.
    • In general, as the threshold increases, the width of the CIs increase, indicating more spread and less confidence in the median bias value, likely related to the decreasing base rate.

Temperature

BCRMSE

    • Regardless of forecast lead time or temporal aggregation, a minimum in the BCRMSE values occurs in the mid-levels (between 300 and 500 hPa) and increases to a maximum at both the near-surface and upper levels.
    • A SS increase in BCRMSE values between the 12-hour and 48-hour forecast lead times is noted. Errors are less than 2.2 C for all lead times.

Bias

    • For all temporal aggregations, a SS cold bias is seen for all lead times at the 850 and 700 hPa levels transitioning to a SS warm bias at and above 500 hPa level with the exception of the 150 hPa level for the winter and spring aggregations at longer lead times.

Dew Point Temperature

BCRMSE

    • As the pressure level decreases from 850 to 500 hPa and the forecast lead time increases from 12 hours to 48 hours, the BCRMSE values increase for all temporal aggregations except winter, where the median value decreases from the 700 to 500 hPa level at the longer lead times.

Bias

    • A SS moist bias is noted for all forecast levels and lead times for all temporal aggregations except summer, which either encompasses zero or has a SS cold bias at 700 hPa depneding on the lead time.

Wind

BCRMSE

    • A general increase from the minimum BCRMSE values at the lowest levels (typically at the 850 or 700 hPa levels) to a maximum at the 300 or 200 hPa level for all forecast lead times and temporal aggregations, is noted.
    • Overall, the errors generally range between 2.5 and 6.5 m/s depending on lead time and temporal aggregation, with a SS increase in BCRMSE values between the 12- and 48-hour lead times seen for several levels.

Bias

    • In general, there is a SS low wind speed bias for all levels at and below 200 hPa, regardless of the forecast lead time or temporal aggregation.
    • The for all seasonal aggregations, except winter, the largest magnitude (low wind speed) bias is observed at 200 hPa.